1. Field of the Invention
The present invention generally relates to an optical disc drive, and more particularly to an optical disc drive which records data on the optical disc and reads the data from the optical disc.
2. Description of the Related Art
There are two types of recordable type optical discs, such as a write-once type and an erasable type. There are several methods to record data on the write-once type optical disc. In one method, Te or Bi is used for the material of a recording layer of the write-once type optical disc and pits are formed on the recording layer by means of melting the material by means of radiating a laser beam to the material. In another method, a thin film composed of a material such as Sb2Se3, TeOx or an organic dye is used for a recording layer of the write-once type optical disc and reflectance of the recording layer is changed by means of radiating a laser beam to the material.
A CD-R disc, which is the write-once type optical disc, has grooves that guide an optical spot. The grooves are wobbled at a center frequency of 22.05 kHz in a radial direction and address information during recording called ATIP (Absolute Time In Pregroove) is also recorded using FSK (Frequency Shift Keying) modulation, which modulates the frequency of 22.05 kHz within a maximum frequency deviation of ±1 kHz.
A recording signal format of the CD-R disc defines the areas that the CD-R disc has. A power calibration area (PCA), a program memory area (PMA), a read-in area, a program area and a read-out area are placed from a position at an inner radius toward a position at an outer radius of the CD-R disc. In the PCA, an optimum recording power is determined by means of writing a signal in the PCA and measuring a reproduced signal from the PCA. In the PMA, information such as signal recording information, skip information and, so on, is temporarily recorded during appending data to the CD-R disc.
To record the data on the CD-R disc properly, an optimum power control (OPC) operation is performed prior to recording the data on the CD-R disc. The strength of the laser beam is set to the optimum recording power value during the OPC operation. One hundred (100) test areas (partitions) are provided in the PCA for performing the OPC operation. Each test area (partition) has 15 frames.
The strength of the laser beam must be set to the optimum power value for each CD-R disc because recording characteristic parameters of one CD-R disc manufactured by one manufacturer are different from those of another CD-R disc that is manufactured by another manufacturer. When the data are recorded on the CD-R disc by means of the laser beam that does not have the optimum power for the CD-R disc, a jitter and an error rate of a reproduced signal might cause the reproduced signal to be degraded.
Conventionally, the signal is recorded using different power of the laser beam for each frame in one test area. For example, 15 levels of power of the laser beam are used for recording the signal to the 15 frames. Then, a peak value (P) and a bottom value (B) of an envelope of each reproduced RF signal from each frame in the test area are detected. Next, a value β=(P+B)/(P−B) is calculated. If the value β is greater than a predetermined value, for example 0.04, the power of the laser beam that is used for recording the signal to the frame from which the RF signal is reproduced is determined to be the optimum power of the laser beam. Then, data are recorded to the CD-R disc using the optimum power of the laser beam. A length of one test area (15 frames) of the PCA is equivalent to a length of about 1.7 revolutions of the CD-R disc track at the inner radius of the CD-R disc.
Further, in the standard of the optical disc, it is prescribed to carry out a running OPC when the data are recorded on the CD-R disc. During the running OPC, strength of a reflected light from a pit portion determined during the OPC operation is compared with the strength of the reflected light from a pit portion during recording data. The running OPC operation is such that a power of the laser beam for recording the data on the CD-R disc is being compensated continuously to keep the optimum recording power or the value β that is obtained during the OPC operation, based on the comparison result mentioned above.
The strength of the reflected light is measured at a back end of the pit portion having a time interval of 11T, where T is about 230 ns (¼.32 MHz) at a standard speed of 1X.
Therefore, it is possible to compensate the power of the laser beam using the running OPC so as to keep the power of the laser beam at the optimum recording power as a sensitivity of the recording layer or a curve of the disc to the laser beam changes from the inner radius toward the outer radius.
However, if the curve of the disc is large, an incident angle of the laser beam to the data area at the outer radius of the CD-R disc is different from the incident angle of the laser beam to the PCA at the inner radius of the CD-R disc. Therefore, an effective laser light to record the data on the CD-R disc at the outer radius of the CD-R disc is so different from that at the inner radius of the CD-R disc that the optimum recording power at the outer radius of the CD-R disc is also different from that at the inner radius of the CD-R disc. Further, the conventional running OPC always compensates the optimum recording power based on the strength of the reflected light from the pit portion so as to become the strength of the reflected light equal to the strength of the reflected light determined by the OPC. Therefore, the recording power is compensated properly at a position of the inner radius of the CD-R disc even if the dye is not coated uniformly or the curve of the disc is large. As a result, the data are recorded properly. However, at a position of the outer radius of the CD-R disc, the actual optimum recording power is completely different from the optimum recording power determined during the OPC. The strength of the reflected light from the pit at the outer radius of the disc is different from the strength of the reflected light from the pit at the PCA of the disc during the OPC. When the data are appended at the position of the outer radius of the disc with the optimum recording power determined by the OPC, it takes a long time to control the actual recording power to become the actual optimum recording power at the outer radius of the disc by means of compensating the recording power using the running OPC. Therefore, it causes the problem that the jitter or the error rate of the reproduced signal becomes high until the recording power is controlled to the actual optimum recording power.
Further, the value β fluctuates at a cycle of revolutions per minute (r.p.m.) of the disc or at a cycle of twice the r.p.m. because of the mechanical characteristics such as dynamic axial runout and so on. Therefore, the strength of the reflected light and the value β measured during the OPC also fluctuate. As a result, the recording power cannot be compensated accurately if the running OPC is performed based on the strength of the reflected light from the pit during the OPC, because the error is included in the measurement value of the strength of the reflected light from the pit during the OPC. As a result, both the error rate and the jitter of the reproduced signal become high because it is impossible to keep the value β of the reproduced signal at the value β determined during OPC if the running OPC cannot keep the recording power at the optimum recording power.